Question : Unable to access a single Domain Name.  ARP timeouts in Sonicwall?

I have a tricky situation, and I've gone through virtually everything I can think of in order to resolve it.  

Starting about a month ago one particular company has been unable to send us e-mails, and neither of us can access the others' websites.  I'm not even sure what info would need to be provided, so I'll post all the relevant information I can think of:

System Info: Both Company's Systems Windows 2003, both running MS Exchange

1) Neither side can access the other's websites.  Lookups provide the IP information, but nothing occurs after that.  The same occurs for pinging (exchange or non-exchange ports).  

2) We can e-mail them, but their e-mails remain stuck in their MS Exchange Queue and eventually die.

3) I cannot telnet to their Exchange port, though I can telnet to the MX record with lowest priority (which does not show as being Microsoft Exchange anyway).  They cannot telnet to our mail server either.  

4) I have checked all firewalls, the main Domain controller, and the router for any rules or restrictions that might be blocking access.  None appears.

5) I've checked both companies for appearing on RBLs, neither appear on any.  

6) Only information I can see in any log, real time or no is an "arp timeout," in my Sonicwall log.  

For instance, if I attempt to access their website, I receive:

03/20/2006     12:58:40.112     ARP timeout     0.0.0.0   x.x.x.xxx (their ip number)

Where 0.0.0.0 is under source and their ip is under destination.

Prior to a month ago both sides could communicate properly, to my knowledge.  Also, nothing has changed on our end in our system setup/layout.

Any help on what I could try next would be greatly appreciated.

Thanks!

Answer : Unable to access a single Domain Name.  ARP timeouts in Sonicwall?

I was just reviewing my notes from the issue we had.
I still think the tech on the other end is resolving.
I know that it has to do with the Exchange SYN/ACK/RST prior to connection.
The tech on the other end couldn't see a problem in his logs either but I sent our logs to Cisco TAC and isolated the issue to the Sonicwall.
I'm 100% sure this is your problem (the Sonicwall).